1. Field of the Invention
The present invention relates to a printing apparatus, and more specifically, to a thermal transfer type printing apparatus which includes a unit for detecting a marker on an ink ribbon.
2. Description of the Related Art
Examples of printer printing methods include thermal transfer, in which ink coated on an ink ribbon is thermally transferred onto printing paper using a thermal head. Examples of a thermal printer, which is a printing apparatus that employs a thermal transfer technique, include printers having a unit for detecting a conveyance position on the ink ribbon.
A method in which a thermal printer detects the conveyance position of an ink ribbon will be described using FIGS. 7 to 11. FIG. 7 is a cross-sectional view of a printing mechanism vicinity in a conventional thermal printer.
A thermal head 101 is fixedly supported on a thermal head unit 150. The thermal head unit 150 is rotatable around a not-illustrated rotation center, and is supported on a main frame of the apparatus body. A platen roller 102 is rotatably supported so as to face a heating element provided on the thermal head 101. The thermal head 101 presses against and separates away from the platen roller 102 according to rotation of the thermal head unit 150.
The thermal head unit 150 is rotated along with the rotation of a head drive lever 110. Control of the rotation amount of the head drive lever 110 is performed by controlling a head drive motor 130 via a not-illustrated drive system.
When a printing operation starts, the head drive lever 110 is rotatably driven a predetermined amount, and the thermal head 101 illustrated in FIG. 7 is moved to a separated state separated from the platen roller 102.
Next, an ink ribbon 105 is wound to perform head-finding conveyance of the ink ribbon, and the head color region (the region onto which the ink of the color to be transferred first is coated) of the ink ribbon 105 is positioned immediately below the thermal head 101.
Next, a pair of conveyance rollers 103 is rotated in a state in which they sandwich a sheet of printing paper 104, and the printing paper 104 is conveyed to a printing start position. Consequently, printing preparation onto the printing paper 104 is completed. The driving of the pair of conveyance rollers 103 and the winding of the ink ribbon 105 are respectively performed by the same conveyance motor 131 via a not-illustrated drive system.
Here, head-finding conveyance of the ink ribbon will be described. FIG. 8 illustrates a partial region of a typical ink ribbon 105. Various colors of ink, for example yellow, magenta, cyan, and an overcoat, are coated on the ink ribbon 105. Between adjacent ones of the regions on which the various ink colors are coated, a light-impermeable black marker 120 is applied.
In the separated state illustrated in FIG. 7, generally, the light emitted from a photoreflector 106 is reflected by a refection plate 107 attached to the thermal head unit 150, and reaches a light reception unit of the photoreflector 106. However, if the black marker 120 coated on the ink ribbon 105 passes above this light path, the light is blocked, and does not reach the light reception unit of the photoreflector 106. Consequently, the black marker 120 can be detected.
Further, as illustrated in FIG. 8, before the ink of the first color (in FIG. 8, yellow) is transferred for the first time during printing, two black markers 120 are printed. Consequently, the head of the ink for the first color and the head of the inks for the other colors can be distinguished. Therefore, when the second black marker 120 is detected as being positioned above the light path of the light from the photoreflector 106, conveyance of the ink ribbon 105 is stopped, and the head-finding conveyance of the ink ribbon is completed.
When the head-finding of the ink ribbon and the head-finding conveyance of the printing paper are completed, the head drive lever 110 is rotatably driven by a predetermined amount. Consequently, as illustrated in FIG. 9, the thermal head 101 moves to a pressing state in which it presses against the platen roller 102. Then, the thermal head 101 selectively causes each heating element to generate heat based on an input image. Along with this, while the pair of conveyance rollers 103 conveys the printing paper 104 in a conveyance direction during printing, a ribbon winding mechanism conveys the ink ribbon 105. Consequently, the ink on the ink ribbon 105 is transferred onto the printing paper 104, whereby a yellow image is formed on the printing paper 104.
Although the ink ribbon 105 which underwent ink transfer is stuck to the printing paper 104 due to heat, the ink ribbon 105 is peeled from the printing paper 104 by conveying it in a different direction from the conveyance direction of the printing paper with a leading edge of a peeling member 108 acting as a starting point.
FIG. 10 illustrates the state when the formation of the yellow image is finished. When image formation is finished, the heat generation from a heating element 151 of the thermal head 101 is stopped. At this stage, the printing paper 104 and the ink ribbon 105 are stuck to each other over a distance A from the heating element 151 to the leading edge of the peeling member 108 (the starting point where the printing paper and the ink ribbon peel from each other). Consequently, while the thermal head 101 is separating from the platen roller 102 (is in the separated state), the printing paper 104 and the ink ribbon 105 are conveyed, and a peeling operation which peels the printing paper 104 and the ink ribbon 105 from each other is actively performed. When the printing paper 104 and the ink ribbon 105 have been sufficiently conveyed and peeled from each other, driving of the conveyance motor 131 is stopped, and the peeling operation is completed.
Next, the ink ribbon 105 is conveyed to the head of the ink for the next color (magenta), and the printing paper 104 is returned to the printing start position. Then, the thermal head 101 is pressed against the platen roller 102 (is in the pressing state), and a printing operation is performed with the ink for the next color.
By repeating this operation, a magenta image and a cyan image are superimposed over the yellow image to form the desired full color image.
FIG. 11 illustrates a positional relationship between the position of the marker 120 printed on the ink ribbon 105 and a region (transfer region R) onto which the ink for each color is applied and which receives the generated heat from the head.
A margin B is provided between the trailing edge of the marker 120 applied on the head of the ink for each color and the leading edge of the transfer region of the ink for the next color. The length of this margin B is illustrated in FIG. 10. This length corresponds to a distance D between the position where the light from the photoreflector 106 reaches and the position of the heating element 151. To perform head-finding of the ink ribbon 105, the leading edge of the transfer region R of the ink ribbon needs to be positioned where the heating element 151 of the thermal head is located at the point when the photoreflector 106 has detected the marker 120.
Further, a margin C is also provided between the trailing edge of the transfer region R and the leading edge of the marker 120 provided at the head of the ink for the next color. This margin C is set to be longer than a length calculated by subtracting the length of the margin B from the conveyance distance of the ink ribbon 105 during the peeling operation. Because of this margin C, after the peeling operation is completed, the photoreflector 106 can detect the marker 120 on the ink ribbon.
If this margin C is not provided, when the peeling operation is completed, the marker 120 at the head of the ink for the next color passes by the light path of the light output from the photoreflector 106. Consequently, after the peeling operation is completed, the marker 120 cannot be detected while the ink ribbon 105 is being conveyed even if an attempt is made to do so. Thus, head-finding of the ink for the next color cannot be performed.
Therefore, for conventional head-finding conveyance of an ink ribbon, it is necessary to form wasteful margins B and C, which cannot be used as the transfer region R. Such margins B and C increase the total length of the ink ribbon 105, leading to an increase in the size of the ink ribbon cassette and in increase in costs. Further, during printing, the ink ribbon 105 has to be needlessly conveyed by the additional length of the margins B and C of the ink ribbon, which increases the time taken for printing.
Further, because the ink ribbon 105 is conveyed more than necessary, the opportunity for wrinkles to form on the ink ribbon 105 increases. The pattern of these wrinkles is printed on the printing paper, which also leads to the problem of an increased risk of the printing quality deteriorating.
In view of the above-described problems, for example, Japanese Patent Application Laid-Open No. 2006-159432 discusses a sensor for detecting a marker on an ink ribbon, which is located between the heating element of the thermal head and a peeling starting point of the peeling member. Light from the sensor is irradiated on the ink ribbon located between the heating element and the peeling member. In this case, since the distance between the position where the light from the sensor is irradiated and the position of the heating element is shortened, the margin B between the marker and the transfer region R of the ink for the next color can be shortened.
In the technique discussed in Japanese Patent Application Laid-Open No. 2006-159432, the light from the sensor irradiates a portion where the ink ribbon and the printing paper are stuck together. Consequently, to detect the marker on the ink ribbon, the sensor light is reflected by the surface of the printing paper. In this case, if the printing paper jiggles around or curls in the printer, the light path of the reflected light reflected by the printing paper diffuses. Therefore, there is the problem that the ink ribbon marker cannot be correctly detected.